Product keys and save data modification are the topics of a recent revision to Japan’s Unfair Competition Prevention Act last month.

The following comes from Gamesindustry.biz as the official information is only in Japanese:

Distributing tools and programs for altering save data
Selling serial numbers or product keys that are unauthorised by the maker of the software in online auctions
Offering services that modify save data on the customer’s behalf

This means those who are able to obtain product keys without authorization from the creator can now be prosecuted in Japan. Those who do can face damage claims for compensating the creator for lost sales, or get fined, “up to ¥5 million [$46k USD], up to five years in prison, or both.” The European Union ruled in 2012 that players who purchased games digitally were able to resell the key should they desire to, but this Japan law appears to be aimed at those who have hacked Steam to gain access to tons of product keys and sold them off online to the highest bidder. The EU is also the reason why Valve was forced to institute its refund policy in 2015, with other distributors such as PlayStation updating cancellation policies for the 14 day threshold period required by the EU.

While combating illicit reselling of product keys is probably a good way to fight hackers from profiting off of auctioning Steam codes, banning save data modifiers seems less productive. Save data modification tools, such as the Cyber Save Editor mentioned in the article are essentially fulfilling the purpose of Game Genie and the like from the 1990’s and 2000’s. As online games rely on data communication between a server and your PSN profile, save data modification’s abuse can’t really give a player an edge in matches of PUBG or Battlefield V. Instead they are useful for helping players beat or get more enjoyment out of single-player games such as God of War, Monster Hunter: World (whose online capabilities are for cooperative play), and Resident Evil 7 by maxing out funds and gear.

Source: Gamesindustry.biz

I'm slightly surprised by this from japan, I know they dislike cheating but to this extent? they need it to make a law to dislike people cheating on non-online games like this? Why?

From a certain perspective, the game itself is a "save data modifier". Regulations like these are short-sighted and naive, if not ignorant. Trying to control what the user does with code or data once it's on their machine is a waste of time, and bound to fail.